1. Field of the Invention
The present invention relates to an optical pickup, and more particularly to an optical pickup including an actuator in which a focusing coil and tracking coils are mounted in a lens holder having an objective lens, and which has magnets for forming magnetic circuits together with the focusing coil and the tracking coils.
2. Description of the Related Art
An optical pickup is used in an optical disk apparatus for effecting recording or reproduction with respect to an optical disk, and a lens holder equipped with an objective lens is mounted on abase member for which access control is provided in a direction along a radial direction of the optical disk. In addition, displacement control is provided for the lens holder in a focusing direction and a tracking direction with respect to the optical disk by the operation of an actuator so as to compensate for a change in the positional relationship between the optical disk and the objective lens in consequence of such as the warpage and eccentricity of the optical disk. A general actuator is constructed by a combination of a focusing coil, tracking coils, and magnets which are mounted on the lens holder supported on the base member displaceably in the aforementioned two directions.
Conventionally, various proposals have been made as to the construction of the actuator of an optical pickup of this type (e.g., refer to JP-A-2000-57600 and JP-A-10-334486). Next, referring to FIGS. 3 and 4, a description will be given of the construction of the actuators disclosed in JP-A-2000-57600 and JP-A-10-334486. It should be noted that in FIGS. 3 and 4 identical or corresponding portions will be denoted by the same reference numerals to facilitate understanding.
FIG. 3 shows the construction of the actuator described in JP-A-2000-57600. In this actuator, a lens holder 2 provided with an objective lens 1 displaceably in the focusing direction and the tracking direction is supported by a fixing member 5a on a base 5 side by means of a suspension 5b. One focus coil 3 and four tracking coils 4 are mounted on the lens holder 2, and plate piece-like permanent magnets 7 are respectively attached to two yokes 6 on the base 5. Further, only a magnetized surface on one surface side of each permanent magnet 7 is opposed to the tracking coils 4 and the focus coil 3 in the same direction, while a magnetized surface on the other surface side is joined to the yoke 6 in a superposed manner. In addition, the focus coil 3 is located on the opposite side to the permanent magnet 7 with the tracking coils 4 disposed therebetween.
FIG. 4 shows the construction of the actuator described in JP-A-10-334486. In this actuator, the focusing coil 3 and the tracking coils 4 are mounted on the lens holder 2 having the objective lens, and the plate piece-like magnet 7 is attached to the yoke 6. Further, only a magnetized surface on one surface side of each magnet 7 is opposed to the tracking coils 4 and the focusing coil 3 in the same direction, while a magnetized surface on the other surface side is joined to the yoke 6 in a super posed manner. In addition, the focusing coil 3 is located on the opposite side to the magnet 7 with the tracking coils 4 disposed therebetween.
In the conventional actuator shown in the above-described JP-A-2000-57600 or the JP-A-10-334486, in each case, only the magnetized surface on one surface side of the magnet (permanent magnet) 7 is opposed to the tracking coils 4 and the focus coil (focusing coil) 3 in the same direction, while the magnetized surface on the other surface side is only joined to the yoke 6 in a superposed manner. Additionally, the focus coil (focusing coil) 3 is located on the opposite side to the magnet (permanent magnet) 7 with the tracking coils 4 disposed therebetween. For this reason, only the magnetized surface on one surface side of the magnet (permanent magnet) 7 contributes to a magnetic circuit formed by the cooperation of the magnet (permanent magnet) 7 and the tracking coils 4, and the magnetized surface on the other surface side does not contribute to that magnetic circuit. Similarly, only the magnetized surface on one surface side of the magnet (permanent magnet) 7 contributes to a magnetic circuit formed by the magnet (permanent magnet) 7 and the focus coil (focusing coil) 3, and the magnetized surface on the other surface side does not contribute to that magnetic circuit.
In the conventional optical pickups described above, the focus coil (focusing coil) 3 is located on the opposite side to the magnet (permanent magnet) 7 with the tracking coils 4 disposed therebetween, only the magnetized surface on one surface side of the magnet (permanent magnet) 7 is used to form the magnetic circuit, and the magnetized surface on the other surface side is not used to form the magnetic circuit. In this situation, however, it has been difficult to efficiently improve both the sensitivity during the operation in the tracking direction and the sensitivity during the operation in the focusing direction by disposing the magnetized surface of the magnet in close proximity to both the tracking coils and the focusing coil.
Namely, even if the sensitivity during the operation in the tracking direction could be improved by disposing the magnetized surface on one surface side of the magnet close to the tracking coils, since the focusing coil is located on the opposite side to the magnet with the tracking coils disposed therebetween, the tracking coils constitute obstructions, and therefore a limitation occurs to disposing the magnetized surface on one surface side of the magnet close to the focusing coil. Hence, it has been difficult to efficiently improve both the sensitivity during the operation in the tracking direction and the sensitivity during the operation in the focusing direction.